1. Field of the Invention
The present invention relates to semiconductor devices and, more particularly, to semiconductor devices which are mounted o substrates on at least one of their respective surfaces (i.e., which are of "surface mounting type").
2. Description of the Related Art
FIGS. 1 to 3 are side views of conventional semiconductor devices ,of the surface mounting type. The illustrated devices are packages having outer leads of different configurations. FIG. 1 shows a small outline package 4a with gull-wing leads, FIG. 2 shows a small outline package 4b with I leads, and FIG. 3 shows a small outline package 4c with J leads.
In each semiconductor device 4a, 4b or 4c, a semiconductor element (not shown) and outer leads (hereinafter abbreviated to "leads") 2a, 2b or 2c electrically connected to the element are molded with resin to form a package body 1a, 1b or 1c. Parts of the leads 2a, 2b or 2c project outward from the package body 1a, 1b or 1c, and the projecting end portions of the leads are formed with soldering portions 3a, 3b or 3c. The semiconductor device 4a, 4b or 4c is mounted on a substrate or the like (not shown) by soldering the soldering portions 3a, 3b or 3c.
The semiconductor devices, which are mounted on the substrates or the like by soldering, entail the following problems when they are subjected to reliability tests such as heat cycle tests where the temperature surrounding the device is varied between high and low temperatures. The semiconductor device 4a or 4b shown in FIG. 1 or 2 entails a problem. Due to the difference in the coefficient of thermal expansion between the package body 1a or 1b and the substrate, cracks are formed in solder (not shown) attached to the soldering portions 3a or 3b. The semiconductor device 4c shown in FIG. 3 entails a problem that since the curved and J-shaped end portions of the outer leads 2c are positioned on the reverse side of the package body 1c and are therefore difficult to see from the front side. Their soldering condition can be checked only with difficulty.